1. Field of the Invention
The subject invention relates to fluid filtration apparatus, and more particular, to a counter top water filtration unit for domestic use.
2. Background of the Related Art
Due to run-off and environmental contamination, drinking water in most areas of the world contains appreciable amounts of dissolved chemicals and suspended particulate material. A number of chemicals and particulates that may be found in drinking water have been associated with possible adverse physiological effects. Other chemicals and particulates in drinking water have been associated with less than desirable taste and sensory perceptions, such as "clouding" of the water or "souring" of the water. Chemicals and particulates in a water source may also lead to undesirable rings in appliances and commodes using large amounts of water, and may result in unsightly films being placed on items washed in the water. In the estimation of many persons, municipal water treatment plants often fail to adequately deal with these problems. In order to improve water quality, many residences and businesses now employ on-site water filters to filter water streams consumed therein.
Until relatively recently, most on-site water filters were typically designed to be mounted in a permanent housing coupled to a water stream, such as in series with a pipe. Such permanent housings were often located in relatively poorly accessible locations (such as under a sink or in the basement) and often required special tools in order to gain access to the filter residing in the housing (such as a wrench). While on-site permanent filters are often perceived to remediate the water sufficiently for everyday uses, such as washing dishes and clothes, there is a large and growing number of people who demand cleaner and more tasteful water for internal consumption. Rather than adding new types of filters into permanent-type on-site water filter housings or increasing the number of such housings, in order to provide for a more convenient manner of coupling filters to water streams and of changing filters, so-called "countertop filtration units" were developed. "Countertop filtration units" are portable filter apparatuses dimensioned to fit on a standard household countertop and adapted for coupling to a fluid flow outlet spigot, such as a faucet. Such units are generally primarily intended for domestic use to filter impurities out of tap water. The unit may be placed on a counter adjacent to a sink.
Countertop filtration units are generally fabricated from plastic and/or metal. Conventionally, these units comprise a base upon which a "sump", such as cup or cover, which acts as a sump, is placed and in which the filter cartridge is housed. The "sump" is generally screwed into the base wherein a seal typically exists to permit fluid tight sealing. The filter in conventional counter filtration units is changed by removing the "sump", pulling out the spent filter, inserting a new filter into the "sump" and reattaching the same to the base. The "sump" has an inlet opening to enable an entrance of the fluid into the "sump" and through the filter materials. The "sump" further has an outlet opening to enable the fluid to be discharged from the "sump" after it has coursed through the filter. The unit may further be equipped with a valve to selectively divert the fluid flowing to the filter cartridge.
Filtration is the process of separating particles from a fluid suspension (liquid or gas) by use of a porous medium or by means of a medium possessing chemical properties, such as hydrophobicity, electrostatic charge, etc., which permit such medium to interact and hold the particles which are to be separated from the fluid while permitting the fluid to pass there through. In conventional filtration, the filter medium retains most of the suspended particles which are filtered on or within itself, but allows the fluid being filtered to pass through unimpeded. Flow across the filter medium is generally achieved by the application of a driving force, usually in the form of a static pressure difference across the filter, which may be generated, for example by external pressure applied upstream, a vacuum applied downstream, gravity, or other force.
Filters used in countertop filtration units are designed to be disposable. One commonplace type of disposable filter is in the form of a solid porous cylinder having a hollow center. When such filters are employed, the fluid to be filtered flows radially through the wall of the cylinder between its exterior and hollow core. Such filters are generally capped at each end with a boundary sealing-cap to permit sealing between the filter and the housing in which it is placed in such a manner as to assure that only fluid having passed through the wall of the filter cylinder and into the hollow core is permitted to exit from the filtration unit. Typically, countertop filtration units employ filters fabricated from granular activated carbon. Granular activated carbon is useful for removing organic chemicals such as chlorine, hydrogen sulfide, pesticides, herbicides, phenol, chlorophenol and hydrocarbon from water. Other filter elements may be employed as well to help remove sediments such as rust and other particles. Silver salts are sometimes added to the filter material to combat bacterial growth. Ion exchange resins are also used in such filtration units.
While carbonaceous filter elements are known to be good at removing contaminants that affect taste, odor of the filtrate, and visible particulate matter, such filters generally are not fine enough to remove bacteria or viruses.
There are numerous microporous elements available for removing bacteria and viruses. Among these elements are hollow fibers having micropores coursing through the fiber walls. Typical microporous hollow fibers include Celgard.TM. manufactured by Questar division of Celanese Corporation. Such hollow fibers offer controlled and relatively uniform porosity as compared to many asymmetric ultrafiltration and microfiltration membranes. Fiber construct is such that there is high membrane surface area-to-volume ratio. The pores in the fibers form tortuous, interconnected channels leading from one surface of the fiber to the other. The pores of these hollow fibers allow the flow of gases and vapors but block passage of many bacteria, colloids and other submicron particles and solutes. Fibers having pores of 0.05 microns or less are capable of filtering most viruses. In order to assure passage of the fluid through the fiber pores rather than through any end, such fibers are generally potted in an epoxy or other standard potting material at both ends of the fiber.
Countertop filter cartridges conventionally can be classified in either of two types: encapsulated and drop-in. Encapsulated cartridges incorporate the "sump", such that the "sump" must be replaced with the filter element. The advantages of encapsulated cartridges are that they are user friendly and the seal between the base and "sump" are replaced each time. There also are advantageous to manufacturers in that they generally require proprietary cartridge replacement. Drop-in cartridges on the other hand are replaced independently of the "sump", the "sump" being re-used each time. The advantage of the drop-in cartridges over encapsulated cartridges is that such cartridges are generally cheaper.
There are problems associated with countertop filtration units employing either encapsulated or drop-in filter cartridges. Both systems require removal of the "sump" from the unit in order to replace the filter. Removal of the "sump" from the base is often less than convenient, given that the "sump" is generally screwed into the base by means of relatively large threads. Further, as most countertop filtration units house the "sump" in an external housing, designed in part to hide the rather non-aesthetic "sump" and inflow/outlet tubes, the external housing must also be removed before access to the "sump" may be had. As the process involved in removing and changing either encapsulated or drop-in filter cartridges is relatively complex, fluid filtration quality often suffers due to less than optimal replacement of the filter. In regard to "drop-in filter cartridges" such filters suffer not only from the problems associated with ease of access to, and replacement of the filter element, but also with respect to the need to continually replace the seal between the "sump" and the base. On the other hand, "encapsulated cartridges," due to the inherent cost of the "sump" which is replaced with each filter change, can be far less than economic.
There is a need, therefore, for an improved countertop filtration unit which permits easy replacement of filter elements and aids in assuring adequate sealing between the "sump" and base.